Can Fish Swim In Space?

When two young fish reached Skylab, they swam in elongated loops, almost like the hands of a clock created by Salvador Dali. In the absence of gravity, they had trouble figuring out which way was up.

By the third day, the fish began to swim in more regular patterns, always positioning themselves with their backs towards the interior lights of Skylab. In many animals, including humans who build rockets, gravity affects special cells in the inner ear that help us sense which way is up (away from gravity). This response is called the vestibular righting response. Since there was no gravity to influence their inner ears, the mummichog fish relied on artificial light to determine their orientation. To the fish, this made sense since sunlight doesn't reach the bottom of the ocean.

The looping behavior in the fish seemed like their version of space sickness. Just like humans and other animals, our inner ears help us balance and stay oriented. When ocean waves or the absence of gravity disrupts these signals, we can become disoriented and even nauseous. As the mummichogs looped, the astronauts experienced nausea and vomiting. However, as the astronauts' nausea subsided, so did the looping behavior in the fish. By the fourth day in space, both the humans and the fish had adapted to their surroundings. The fish swam in their small plastic aquariums in space as though they had always been there.

The question remained: would the unhatched fish be susceptible to space sickness and loop when they hatched? The astronauts discovered the answer during their third week on Skylab when 48 out of 50 eggs hatched. Surprisingly, these tiny mummichog fry did not loop. They immediately followed the behavior of their older counterparts, using the light for orientation. It seemed that the fish fry had learned the trick that up is where the light comes from while they were still embryos. Only when the astronauts shook the aquarium did the fish fry, seemingly disoriented, begin swimming in loops, but they soon reverted to swimming with their backs to the light.

What Happens To Fish Anatomy In Space?

To closely examine how the fish responded to life in space, scientists genetically altered them so that two types of cells in their bodies would emit different colours of light under specific wavelengths. The first type, called osteoclasts, breaks down bone tissue as part of the process of repairing and maintaining any damage. The second type, osteoblasts, creates the structures that bones form around.

Once the fish arrived at the International Space Station (ISS), they were placed in a specialised tank designed for microgravity. Researchers observed them from a remote laboratory at the Tsukuba Space Center, using two different fluorescent lights to monitor how their bodies adapted to the new environment.

Remarkably, the fish quickly responded to their new living conditions, allowing the researchers to almost instantly observe the effects of microgravity on their bodies. Both types of cells multiplied noticeably compared to a control group on Earth, and certain genes were activated in ways not typically seen under normal gravity.

Why Were Medaka Fish Chosen To Go To Space?

For a number of years, scientists from the Japanese Space Agency (JAXA) conducted research on how life in the International Space Station affected a group of small medaka fish. These fish, also called Japanese rice fish, are native to Japan and hold great value for space research. They are not only simple to breed but also transparent, providing researchers with a clear view of their bones and internal organs as they adapt to life in space.

What Equipment Do You Need In Space For Fish?

Aquariums provided a relaxing pastime for humans on Earth, but recreation was not the goal behind the Aquatic Habitat, or AQH, aboard the International Space Station. Instead, researchers used this unique facility to examine how microgravity impacted marine life.

Sponsored by the Japanese Space Agency, or JAXA, the habitat was a closed-water circulatory system that provided a new facility option for station research. Scientists used the habitat to study small, freshwater fish in orbit, particularly the Medaka (Oryzias latipes) fish, for their first investigations.

Scientists had multiple studies planned to investigate the impacts of radiation, bone degradation, muscle atrophy, and developmental biology. These investigations could last up to 90 days and provide data that might lead to a better understanding of related human health concerns on Earth.

"We thought studies on bone degradation mechanisms and muscle atrophy mechanisms were applicable to human health problems, especially for the ageing society," said Nobuyoshi Fujimoto, associate senior engineer at JAXA's Space Environment Unitization Center

Medaka fish were ideal specimens for many reasons. They were transparent, making it easy to view the inner workings of their organs. They also bred quickly and easily in microgravity environments, enabling multi-generation studies. Researchers could take advantage of various genetic modifications in these fish. Additionally, scientists already had the entire Medaka genome identified, making it easier to recognize any alterations to the fish's genes due to factors like space radiation.

The habitat resided in the Japanese Experiment Module, or JEM, also known as Kibo, which means "hope" in Japanese. It was attached to a multipurpose small payload rack for power and housing. The AQH was launched on July 20, with the third Japanese H-II Transfer Vehicle, or HTV cargo vehicle flight, also called Konotouri.

This facility included an improved water circulation system that monitored water conditions, removing waste, and ensured proper pressure and oxygen flow rates. The system's design upgrades were based on lessons learned from previous habitats that flew on space shuttle missions STS-47, STS-65, and STS-90.

"In order to keep water quality in good condition for the health of the fish, we had to do many tests on the filtration system, especially the bacteria filter," said Fujimoto. "The special bacteria filter purified waste materials, such as ammonia, so that we could keep fish for up to 90 days. This capability made it possible for egg-to-egg breeding aboard the station, which meant up to three generations could be born in orbit. This was a first for fish in space."

The habitat provided automatic feeding for the fish, air-water interface, temperature control, and a specimen sampling mechanism. There were two chambers for habitation, each sized at 15 by 7 by 7 cm, holding about 700 cc of water and a stabilized area for oxygen that enabled fish to "peck" air. LED lights simulated day and night cycles, while two video cameras recorded images of the fish to downlink to the ground upon request.

The air-water interface design also made it possible for the AQH to potentially house amphibians in future studies, although currently planned investigations only used fish. Small plastic plates at the upper side of each aquarium used a grid structure to trap a small amount of air, injected by the crew at the start of an investigation. The design, which was tested using parabolic flights, prevented the water from escaping into the microgravity environment

When researchers were ready for the fish to participate in orbit, they travelled in a special transport container to the station, where the crew then installed them within the habitat for observation. While the AQH was not specifically an aquarium, the crew might have enjoyed a sense of relaxation in viewing the fish as they went about their duties aboard the orbiting laboratory.